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These estimates seem kind of crazy, unless we've suddenly gotten way better at measuring defense. I think someone will have this number of runs above average, and I think these are the most likely guesses as to who the best defenders will be, but to project ahead of time that Simmons is going to be 3 wins better on defense than the average shortstop, based on basically one year of data, seems really farfetched to me.

Bill James Online posts John Dewan's defensive numbers and projections, which state that the spread in defensive value can be 40 or 50 runs between two players at the same position. At the same time, James himself has stated relatively recently that he finds these large differences in fielding value to be hard to swallow.

Because of the difference between them in range, however, Baseball Reference estimates that Parker in 1986 was 17 runs worse in the outfield than an average right fielder, whereas Evans was eight runs better. That’s 25 runs.

I don’t know how they calculate that, and, because defense is so hard to measure, I prefer to use more conservative measurements. The difference between an average team and a championship team, in a season, is only about 150 runs. Saying that the fielding difference between two right fielders is 25 runs is a little like saying that a 150-pound woman gave birth to a 25-pound baby. Ouch. I’m not saying it’s not possible; it’s just hard to believe. I have Evans as being only about eight runs better than Parker in the field, not because I don’t believe the 25-run difference is possible, but just because I just don’t think that we know for certain how large the difference was.

I confess that I find this juxtaposition and apparent contradiction to be a little humorous. Reasonable minds can and do disagree on these matters, of course.

I seem to recall James answering a question in his mailbag in the last six months or so in which he said that his system caps fielding value at about 10 runs above average or so. That's not verbatim, and I might be off by a quite bit, but that's vaguely what I remember. If someone is a subscriber and can search the mailbag archives, then he might be able to find the quote.

I was going snark about how there were no Tigers on the list, then I read this:

The Tigers were horrible defensively in 2013, losing 63 runs over the course of the season. The biggest reason they are going to be much better this year is addition by subtraction. Subtract Fielder’s 13 runs lost at first base by moving to Texas, and subtract Cabrera’s 18 runs lost at third base by moving over to his better defensive position, first base, and you get vast improvement. Now add in Ian Kinsler at second base, a return to form defensively from Torii Hunter, and a full season from Jose Igelsias at shortstop, and the Tigers go from one of the worst to one of the best defensive teams in baseball in one season.

James sez the Tigers have gone from -63 to +26, an 89 run difference...that's almost nine whole games, people. (I'll take it.)

James sez the Tigers have gone from -63 to +26, an 89 run difference...that's almost nine whole games, people. (I'll take it.)

By UZR the Rays went from -48.2 in 2007 to 72.6 in 2008. BBRef doesn't show a total column for DRS but by Total Zone they went from -79 to 54 (-6.6 to 2.6 dWAR). It was a positively ridiculous turnaround and the biggest reason for them surprising in 2008.

DRS is defensive runs saved versus an *average* player at that position (more or less).

As I understand it, a player gets positive credit for making plays and negative credit for failing to make plays, with the amount of credit dependent on the frequency with which that play is successfully made. So if a player were to make 90% of the plays that his peers make 90% of the time, 50% of the plays that his peers make 50% of the time, and 10% of the plays that his peers make 10% of the time (and so on), then he'd be an exactly average fielder and his DRS would be 0.